Mobile radio technology is experiencing rapid development. Work is presently proceeding on standardizing what is called the UMTS mobile radio standard (“Universal Mobile Telecommunication System”) for mobile radio sets of the third mobile radio generation.
In order to match the bit rate to the transmission rate respectively possible, rate matching is carried out in the transmitter, in which case either bits are removed from the bit stream or multiplied, in particular doubled, in the bit stream. The removal of bits is denoted as “puncturing” and the multiplication as “repetition”.
It is generally ensured when puncturing or repeating that the bits are punctured or repeated as uniformly as possible. Known for this purpose are algorithms in the case of which the bits of a bit stream are combined to form frames, and there is determined in each case for the bits of the individual frames an updated error value that constitutes a measure of the deviation between the instantaneous puncturing or repetition rate and the desired puncturing or repetition rate. It is then decided as a function of this updated error value whether the corresponding bit is to be punctured or repeated.
The calculation of the updated error value is performed in this case as a function of an error value, calculated for a preceding bit, and constant update parameters.
However, a non-uniform distribution of the punctured or repeated bits also can be of interest for specific applications.
Thus, for example, it can be desirable to transmit specific bit ranges (termed “Class A Bits”) with a better quality than other bit ranges (so-called “Class B Bits” or “Class C Bits”). This is of particular relevance for speech transmission. This problem was solved for AMR coders (“Adaptive MultiRate” coders) in GSM (“Global System for Mobile Communications”) systems by heuristically determining a puncturing pattern that provided for the range of class A bits a stronger puncturing than for the ranges of class B or class C bits. However, there are two reasons why this procedure cannot be applied to UMTS systems. Firstly, in the case of UMTS systems, the total number of bits to be punctured or the total number of bits to be transmitted is not fixed a priori, but depends on the totality of the services to be transmitted. Secondly, the puncturing, at least in the case of an uplink connection and in the TDD (“Time Division Duplex”) mode, always must be carried out after a first interleaving operation, with the bits in all frames needing to be punctured uniformly.
A further application for a non-uniform puncturing is what is called “tail puncturing”. If, as is generally customary, convolution coding is applied for channel coding, the bits at the start and at the end of a frame are more effectively protected against transmission errors than the bits present in the middle frame region. However, this is, in part, not required at all.
A more uniform error distribution, and thus an overall better transmission performance, then can be achieved by a stronger puncturing in the edge regions of the frame.
It is, therefore, an object of the present invention to propose a method for matching the bit rate, and a corresponding communication device, a non-uniform distribution of the punctured or repeated bits being possible with the smallest possible outlay.